#include <fstream>
#include <string.h>
#define MAX 1105
using namespace std;

ifstream fin ("barbar.in");
ofstream fout ("barbar.out");

const int x[4]={-1,0,0,1};
const int y[4]={0,-1,1,0};

int a[MAX][MAX],n,m,xi,xf,yf,yi,ii[3000001],jj[3000001],numar,ok=0,minim;

void citire()
{
    char s[1010];
    fin>>n>>m;
       fin.getline(s,1030);
    for (int i=1;i<=n;i++)
    {
	fin.getline(s,1010);
	for (int j=0;j<=m;j++)
	    if (s[j]=='*')
	       a[i][j+1]=-1;
	    else
	       if (s[j]=='D')
	       {
		 ii[numar]=i;
		 jj[numar]=j+1;
		     a[i][j+1]=1;
		 numar++;
	       }
	       else
		 if (s[j]=='I')
		 {
		    xi=i;
		    yi=j+1;
		 }
		 else
		   if (s[j]=='O')
		   {
		      xf=i;
		      yf=j+1;
		   }
    }
}

int min (int a,int b)
{
   if (a<b)
      return a;
   return b;
}

void lee ()
{
    int nr=numar;
    for (int i=0;i<nr;i++)
      for (int k=0;k<4;k++)
	 if (a[ii[i] +x[k]][jj[i] +y[k]]==0 ){
	   a[ii[i] +x[k]][jj[i] +y[k]] = a[ii[i]][jj[i]]+1;
	   ii[nr]=ii[i]+x[k];
	   jj[nr]=jj[i]+y[k];
	   nr++;
   }
}

void fct()
{
   int max=n;
   if (m>n)
      max=m;

   for (int r=0;r<=max;r++)
   {
      a[r][0]=-1;
      a[r][m+1]=-1;
      a[n+1][r]=-1;
      a[0][r]=-1;
   }
   lee();
}

void caut()
{

	 int max=-1;
	 for (int q=1;q<=n;q++)
		    for (int w=1;w<=m;w++)
				  if (a[q][w]>max)
					     max=a[q][w];
    minim=max;
}

int main ()
{
	   minim=0;
   citire();
   fct();
   caut();
   fout<<minim-1<<"\n";
   fout.close();
   return 0;
}